# -*- coding: utf-8 -*-
"""
Created on Fri May 17 15:45:01 2024

@author: Administrator
"""


def san_jiao_mian_ji(a,b,c):
    if a + b > c and a + c > b and b +c > a:
        san_jiao_mian_ji = 0
        p = (a + b + c) / 2
        san_jiao_mian_ji = (p * (p-a) * (p-b) * (p-c)) ** 0.5
        return san_jiao_mian_ji


a = float(input("请输入第一条边长："))
b = float(input("请输入第二条边长："))
c = float(input("请输入第三条边长："))
area = san_jiao_mian_ji(a,b,c)
print()